From your link: "What the evidence supports is a population in which average life expectancy at age 10 was approximately 35 to 37 years.
This figure may be taken, I think, as relatively secure for the general Roman population, with an exception being made only for the affluent elite whose life expectancy may well have been considerably higher."
So, if we may suppose a cemetery of mostly "affluent elite", then an average age there of 45 might not be so unexpected.
Thanks Bro’!